Development of future tropical cyclone 100-year floodplain in a changing climate

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Matthew V. Bilskie, Scott Hagen, Jennifer L. Irish

Thursday 2 july 2015

16:00 - 16:20h at Antarctica (level 0)

Themes: IAHR/COPRI Symposium on Long Waves and Relevant Extremes

Parallel session: 13D. COPRI Symposium: Long waves and relevant extremes

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Global sea levels are estimated to rise between 0.2 m and 2.0 m by the year 2100 (Parris et al., 2012) and in conjunction with tropical cyclones, flood risk is projected to increase (Lin et al., 2012). As the rate of sea level rise increases, the coast and coastal land margins will likely be altered in a dramatic fashion (e.g., increased morphology and wetland migration) with increased population densities. To assess the accelerated flood risk, a methodology is developed to estimate the 100-year floodplain for the year 2100 under two extremes of climate change scenarios for the northern Gulf of Mexico spanning the Mississippi, Alabama and Florida panhandle coasts. In the past decade, the Federal Emergency Management Agency (FEMA) has produced present day digital flood insurance rate maps (DFIRMs) in this region; from this work, there exists a large population of synthetic tropical cyclones that include varying tropical cyclone characteristics (i.e., forward speed, radius to maximum winds, etc.). We utilize the joint probability method with optimal sampling (JPM-OS) (Resio et al., 2009) to reduce the total number of synthetic storms necessary in order to develop the 100-year flood surface elevation. To simulate the short- and long-wave dynamics, a high-resolution SWAN+ADCDIRC model containing 5.5 million computational points was developed and is forced by the reduced set of synthetic tropical cyclones . The storm surge model is initialized based on estimates of future shoreline and dune positions and heights, wetland evolution, and land use land cover (LULC) for the year 2100 according to a given sea level rise scenario. Storm surge simulations are performed for a low (0.2 m) and a high (2.0) sea level rise (SLR) scenario (Parris et al., 2012). The resulting simulated maximum water surface elevations are analyzed, and the 100-year floodplain is extracted for each of the two SLR scenarios. The results will assist coastal resource managers and planners on the possible risk of future tropical cyclone flooding under an extreme range of potential outcomes.